Infrared gas analyzing apparatus



Jan. 22, 1952 A. E. MARTIN INFRARED GAS ANALYZING APPARATUS Filed Oct. 9, 1948 Patented Jan. 22, 1952 INFRARED GAS ANALYZING APPARATUS I I Albert Edward Martin, Newcastle-on-Tyne, England, assign'or to C. A. Parsons & Company Limited, Newcastle-omTyne, England Application October 9, 1948, Serial No. 53,678 In Great Britain October 9, 1947 3 Claims. (Cl. 250-83) This invention relates to infra-red gas analysers of the kind wherein infra-red rays are passed by way of a rotary shutter device through two gas filled tubes fitted at each end with windows transparent to these rays, the rays afterwards acting upon the contents of two chambers partitioned from one another by a thin metal diaphragm adjacent to a fixed electrode.

In such instruments the two latter chambers are filled with the gas to be detected and energy is absorbed as radiation passes through them ac-- cording to the nature of infra-red absorption of the gas in question. As the gas heats up an increase of pressure is produced and any difference between the pressures in the two chambers causes the diaphragm to deform and so gives rise to changes of capacity in respect to an insulated perforated metal plate which is fixed in close proximity to the diaphragm.

The radiation from the heaters passing through the two absorption tubes into the chambers is interrupted by a rotating shutter which admits radiation simultaneously to the tubes, and if both these contain gas with no infra-red absorption, the pressure pulses in the chambers will balance and no movement of the diaphragm will result, but if some of the gas to be detected is passed into one of the absorption tubes, energy will be absorbed before it can reach the corresponding detecting chamber. The balance will now be upset and the diaphragm will vibrate at the frequency of interruption of the radiation. The capacity changes are amplified electronically and finally an indication is obtained on a meter which can be calibrated in gas concentration.

In such instruments it is customary to fill the detecting chambers with the gas to be detected, this gas being heated to a greater or lesser extent by the infra-red radiations absorbed during their passage through the detecting chambers.

The object of the present invention is to provide improved forms of such apparatus wherein there need be no question of change of sensitivity with time on account of a leakage of gas and wherein an extended range of compounds may be detected.

The invention consists in gas analysers embodying features as set forth in the claims appendant hereto.

In carrying the invention into effect according to one form illustrated by way of example in the accompanying drawing, I provide two nichrome heaters an. adjacent respectively to transparent windows be at one end of each of two absorption tubes de furnished also at the other end with transparent windows jg. The latter windows are disposed respectively adjacent to two chambers hi separated from each other by a thin metal diaphragm 1 adjacent to a fixed insulated perforated plate is. The chambers hi are furnished with transparent windows mn and are filled with the gas to be detected and energy is absorbed as radiation passes through them according to the nature of infra-red absorption of the gas in question. As the gas in the chambers heats up an increase of pressure is produced causing the diaphragm 7 to deform. The balance will be upset and the diaphragm will vibrate at the frequency of interruption of the radiation, this interruption being produced by a rotary shutter device 0 which admits light simultaneously to the two absorp:-

tion tubes.

In accordance with the present invention solid material, preferably in the form of thin film p is provided in the detecting chambers hi in place of or in addition to an absorbing gas. Absorption takes place in the solid film or films which thereby suffer a rise in temperature, and in turn the air or other gas in the vessel is heated by conduction from the solid material. In this way a pressure increase is produced in the detecting chamber each time radiation enters, exactly as with the usual gas filled detecting chambers. There need be no question of change of sensitivity with time on account of a leakage of gas, since the gas is merely used to convert the temperature rise of the solid film into a pressure increase and air can be used for this purpose.

Solids with specially desirable absorption characteristics can be used where difiiculty would be found in finding a gas or gases with equally suitable characteristics. For example, polythene (polyethylene) films could be used for an instrument designed to measure CH2 groups in organic compounds. Such films consist essentially of long chains of CH: groups.

I claim:

1. In gas analysing apparatus wherein infrared rays are passed by way of a rotary shutter device through two gas filled tubes fitted at each end with windows transparent to these rays, the rays afterwards acting upon the contents of two detecting chambers partitioned from one another by a thin metal diaphragm adjacent to a fixed electrode, the provision in the detecting chambers of solid material for absorbing infra-red radiations, the

detecting chambers being arranged to hold gas for heating by the solid material and exerting pressure on the diaphragm.

2. Gas analysing apparatus as claimed in claim 1, wherein said solid material is in the form of a thin film.

3. Gas analysers as claimed in claim 2 wherein said thin film is coxnposed of polyethylene.

ALBERT EDWARD MARTIN.

REFERENCES CITED The following references are. of record in the file of this patent:

UNITED STATES PATENTS Pfund 20, 1940 4 Number Name Date 2,424,976 Golay et a1 Aug. 5, 1947 2,431,019 Barnes Nov. 18, 1947 2,435,519 Tolson Feb. 3, 1948 2,451,019 Moore Nov. 18, 1948 2,456,801 Tolson Dec. 21, 1948 (STHER REFERENCES An Optical-Acoustic Method of Gas Analysis by 10 Callisen, Nature, Feb. 1, 1947, page 167.

et 9.1., Journal of. the Optical Society of America,

pp. 199-200,Ap1='. 1946. 

